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Sildenafil Medication

Sildenafil Medication

What is sildenafil?

Sildenafil is an oral medication called a phosphodiesterase-5 (PDE5) inhibitor approved for the treatment of pulmonary arterial hypertension (PAH) in World Health Organization (WHO) Group 1 patients. The goal of this therapy is to improve exercise ability and delay clinical worsening. Research studies showing the effectiveness of the medication included mostly patients with symptoms that were rated as WHO Functional Class II-III.Sildenafil is marketed as Revatio® for PAH and was approved by the United States Food and Drug Administration (FDA) in 2005. Sildenafil is also marketed as Viagra® which is FDA-approved for the treatment of erectile dysfunction but not for the treatment of PAH.

How does sildenafil work?

PDE5 is a substance produced in the lungs and other parts of the body that breaks down another substance called cyclic guanosine monophosphate (GMP). Cyclic GMP causes the blood vessels (arteries) to relax and widen. Sildenafil decreases the activity of PDE5, so that more cyclic GMP is available for the blood vessels inside the lungs. This leads to relaxation, or widening, of those vessels. Relaxing and widening of the blood vessels in the lungs decreases the pulmonary blood pressure to the heart and improves its function. This reduces blood pressure in the lungs which generally results in the ability to be more active. Research studies have verified this improvement.

What are the frequent side effects of sildenafil?

Sildenafil is generally well tolerated. The most frequent side effects are:

Nose bleeds

Headache

Upset stomach and heartburn

Flushing of the skin

Difficulty sleeping

Worsening shortness of breath

Nasal congestion.

Can men and women take sildenafil?

Yes, studies have evaluated sildenafil in both men and women with PAH, and no differences in side effects have been reported between genders. Studies have not shown any effect on sexual function in women who have taken sildenafil.

Vision and Hearing Issues

There are reports from studies done with Sildenafil for erectile dysfunction describing very rare hearing and vision problems. All patients should be educated that if they experience hearing or vision changes to talk with their pulmonary hypertension specialist promptly. In my experience, mild vision and hearing complaints are not uncommon but when evaluated they tend to be explained by wax impaction in the ear or cataracts that are not related to pulmonary hypertension medications or need for a new eye glass lens prescription.

Mechanism of action

Sildenafil inhibits the cGMP-specific phosphodiesterase type 5 (PDE5) which is responsible for degradation of cGMP in the corpus cavernosum located around the penis. Penile erection during sexual stimulation is caused by increased penile blood flow resulting from the relaxation of penile arteries and corpus cavernosal smooth muscle. This response is mediated by the release of nitric oxide (NO) from nerve terminals and endothelial cells, which stimulates the synthesis of cGMP in smooth muscle cells. Cyclic GMP causes smooth muscle relaxation and increased blood flow into the corpus cavernosum. The inhibition of phosphodiesterase type 5 (PDE5) by sildenafil enhances erectile function by increasing the amount of cGMP.

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